Water glass is traditionally made by melting silica sand with sodium or potassium carbonate at a very high temperature and then dissolving the finely divided solidified product in water. Thus water glass can be considered an ecologically acceptable substance to include in construction materials, such as a binder in mineral wool products or in cementitious products. Water glass has also been used as a binder in raw material briquettes for mineral wool production, or as binders for making foundry molds or cores, or for use as coating substances and adhesives. Thus for example DE 28 04 069 refers to a method of producing an insulating product by binding mineral fibres with water glass.
One disadvantage relating to the use of water glass is, however, that its manufacture uses pure raw materials and is very energy consuming. Another disadvantage is that such water glass is a highly alkaline product, which can cause stability problems, for example when used as a binder in cementituous products. Water glass typically has a RB ratio (the molar ratio SiO2/Na2O) of from appr. 1 to 4, the ratio of commercial water glass being typically appr. 3.3.
It is also known to use a mixture of water glass with other substances for various purposes, such as with clay or cement as a binder for mineral wool products, see e.g. SE 420 488. Such a product, although providing good water and heat resistance, has poor compression resistance, is brittle and causes dusting. The EP B 466 754 on the other hand describes the use of a binder made from slag activated with water glass for making a temperature and moisture resistant mineral wool product which is also capable of withstanding high temporary loads.
EP 59 088 describes high alkali silicate solutions to be used for binding purposes, especially for foundry moulds and cores, which solutions are made by dissolving finely divided silica powder into an alkaline solution, the resultant solution having a Rs value of 1.6 to 3.5. The silicate solutions so prepared have a low alumina content, typically below 2% .